There were two issues in this PR:

1) We were crashing in is_really_empty_class because we say that the
internal RTTI types are classes, but never gave them TYPE_BINFO.

2) We were allowing the cast to a different pointer type because STRIP_NOPS
in cxx_fold_indirect_ref ignored REINTERPRET_CAST_P.

	* rtti.c (get_tinfo_desc): Call xref_basetypes.
	* constexpr.c (cxx_fold_indirect_ref): Don't strip
	REINTERPRET_CAST_P.